Display devices convert electrical signals into light levels that make up a displayed image. Digital display devices are a subset of display devices, and are capable of displaying a finite number of discrete light levels, or gray shades, at any instance in time. Binary (two state) displays are a subset of digital display devices that can display only two light levels at any instance in time, the two light levels being fully on or fully off.
Video display devices can show a sequence of images, providing the appearance of moving pictures. Video display devices can be analog, digital, or binary.
Examples of digital display devices include: the Digital Micromirror Device (DMD) from Texas Instruments (Dallas, Tex.), the Digital Liquid Crystal on Silicon (D-LCOS) device, the VueG8 technology from Syndiant (Dallas, Tex.), and the Plasma Display Panel (PDP), and light emitting diode (LED) displays. Some analog imaging devices can also be operated as a digital display, including the D-ILA device from JVC-Kenwood (Kanagawa, Japan).
A video source provides video signals to a display. The video is comprised of a sequence of images, or frames. Video signals can be analog or digital and can be converted between analog and digital forms.
An image or video frame is composed of rows and columns of pixels. The rows are also referred to as lines. Each pixel of a digital video frame has associated data that represents the light intensity and, in multicolor displays, the color of the pixel. The data is comprised of one or more binary bits (zeroes or ones). The value each bit represents may be a binary weighting (powers of 2), or some other, possibly arbitrary, weighting.
The typical structure of digital video feeding a display is a stream of digital values representing the light level to be displayed for each video pixel. Typically, the order of the pixels in the stream is from left to right for an entire line (i.e. row) and then moving down one line and repeating for every line in the display. This ordering of pixels is referred to herein as “video order.”
Each image, or video frame, is displayed for an amount of time called the frame time. The frame time can be subdivided into time slots, known as bit segments. A digital display shows each bit segment for an amount of time that is proportional to the desired weight of the bit segment. The bit segments can be all the same weight (i.e. length in time), or they can vary by segment. If the illumination is variable, this will also affect the weight of the bit segments. Some digital displays (e.g. DMD) can produce shorter bit segments if one or more adjacent bit segments are lengthened. Short bit segments are desired for high effective bit depth, but require more data bandwidth and device speed.